Biochem - Metabolism (Glycolysis)

Question 1

What is the first step of glycolysis? For what other process is this the first step, and where is this particular process located?

Answer 1

Phosphorylation of glucose to yield glucose-6-P serves as the 1st step of glycolysis (also serves as the 1st step of glycogen synthesis in the liver).

Question 2

Again, what is the first step of glycolysis? What catalyzes this step, and on what does this generally depend?

Answer 2

Phosphorylation of glucose to yield glucose-6-P serves as the 1st step of glycolysis (also serves as the 1st step of glycogen synthesis in the liver); Reaction is catalyzed by either hexokinase or glucokinase, depending on the tissue.

Question 3

What activity does hexokinase have at low glucose concentrations? What happens at high glucose concentrations?

Answer 3

At low glucose concentrations, hexokinase sequesters glucose in the tissue. At high glucose concentrations, excess glucose is stored in the liver.

Question 4

What is the location of hexokinase versus glucokinase?

Answer 4

HEXOKINASE: Most tissues, but not liver nor Beta cells of pancreas; GLUCOKINASE: Liver, Beta cells of pancreas

Question 5

What is the Km of hexokinase versus glucokinase?

Answer 5

HEXOKINASE: Lower (higher affinity); GLUCOKINASE: Higher (lower affinity)

Question 6

What is the Vmax of hexokinase versus glucokinase?

Answer 6

HEXOKINASE: Lower (lower capacity); GLUCOKINASE: Higher (higher capacity)

Question 7

Is hexokinase versus glucokinase induced by insulin?

Answer 7

HEXOKINASE: No; GLUCOKINASE: Yes

Question 8

Is hexokinase versus glucokinase feedback-inhibited by glucose-6-P?

Answer 8

HEXOKINASE: Yes; GLUCOKINASE: No

Question 9

Is hexokinase versus glucokinase gene mutation associated with maturity-onset diabetes of the young (MODY)?

Answer 9

HEXOKINASE: No; GLUCOKINASE: Yes

Question 10

Where does glycolysis occur? What is its net equation? What is important to note about the equation?

Answer 10

Net glycolysis (cytoplasm): Glucose + 2 Pi + 2 ADP + 2 NAD+ => 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O; Equation not balanced chemically, and exact balanced equation depends on ionization state of reactants and products.

Question 11

What are 2 key glycolysis enzymes that require ATP? What is important to remember about each of these enzymes?

Answer 11

(1) Hexokinase/Glucokinase (Glucokinase in liver and Beta cells of pancreas; Hexokinase in all other tissues) (2) Phoshofructokinase-1 (rate-limiting step)

Question 12

What glycolysis reaction does hexokinase/glucokinase catalyze?

Answer 12

Glucose => Glucose-6-phosphate

Question 13

What are the negative regulators of Hexokinase versus glucokinase?

Answer 13

HEXOKINASE: Glucose 6-P; GLUCOKINASE: Fructose-6-P

Question 14

What glycolysis reaction does phosphofructokinase-1 catalyze?

Answer 14

Fructose 6-P => Fructose-1,6-BP (rate-limiting step)

Question 15

What are the positive and negative regulators of Phosphofructokinase-1?

Answer 15

POSITIVE: AMP, Fructose-2,6-BP; NEGATIVE: ATP, citrate

Question 16

What are 2 key glycolysis enzymes that produce ATP?

Answer 16

(1) Phosphoglycerate kinase (2) Pyruvate kinase

Question 17

What glycolysis reaction does phosphoglycerate kinase catalyze?

Answer 17

1,3-BPG => 3-PG

Question 18

What glycolysis reaction does pyruvate kinase catalyze?

Answer 18

Phosphoenolpyruvate => Pyruvate

Question 19

What are the positive versus negative regulators of Pyruvate kinase?

Answer 19

POSITIVE: fructose-1,6-BP; NEGATIVE: ATP, alanine

Question 20

What are 2 enzymes that allow regulation of gluconeogenesis/glycolysis by F2,6BP? Which is active in fasting versus fed states?

Answer 20

(1) Fructose bisphosphatase-2 (active in fasting state) (2) Phosphofructokinase-2 (active in fed state)

Question 21

How do FBPase-2 and PFK-2 compare/contrast in terms of general structure/function?

Answer 21

FBPase-2 and PFK-2 are the same bifunctional enzyme whose function is reversed by phosphorylation by protein kinase A

Question 22

What happens to glycolysis versus gluconeogenesis in the fasting state? Briefly detail the mechanism by which this occurs.

Answer 22

Fasting state: Increase glucagon => increase cAMP => increase protein kinase A => increase FBPase-2, decrease PFK-2, less glycolysis, more gluconeogenesis

Question 23

What happens to glycolysis versus gluconeogenesis in the fed state? Briefly detail the mechanism by which this occurs.

Answer 23

Fed state: Increase insulin => decrease cAMP => decrease protein kinase A => decrease FBPase-2, increase PFK-2, more glycolysis, less gluconeogenesis

Question 24

Draw a digram relating regulation by F2,6BP to FBPase-2, PFK-2, glycolysis, and gluconeogenesis.

Answer 24

See p. 102 in First Aid 2014 for visual in middle of page